热机耦合下低速柴油机活塞蠕变-疲劳寿命

Creep-Fatigue Lifetime of a Low-Speed Diesel Engine Piston Based on Thermo-Mechanical Coupling

为分析船用低速机活塞在热-机械负荷作用下导致的失效,以低速柴油机活塞为例,推导了高温蠕变和热机耦合疲劳同时作用下的损伤累积模型和寿命预测方程,建立了活塞温度场计算模型,并结合温度场测试进行了验证,对最大连续运行工况(MRC)和超负荷工况(OR)下活塞的温度场、热应力、热变形和热机耦合应力进行了分析,对蠕变-疲劳损伤下的活塞寿命进行了评估.结果表明:活塞温度场仿真与测试的误差在5%以内,活塞在100%负荷条件下纯蠕变寿命约为46500 h,危险点位于活塞顶面喉口附近高温区,纯疲劳寿命约为38400 h,危险点位于活塞与活塞杆接触面边缘;而在蠕变-疲劳复合损伤状态下,活塞的服役寿命降至21000 h,较纯蠕变寿命降低54%,较纯疲劳寿命降低45%,危险点位于活塞温度较高且热应力相对较大的活塞顶面燃烧室盆部区域.

In order to analyze the failure of a low-speed marine engine piston under the combined action of thermal and mechanical loads,a damage accumulation model and life prediction equations were deduced under the simultaneous action of high-temperature creep and thermo-mechanical coupling fatigue.The numerical model of the piston temperature field was developed and verified against experimental results.The temperature field,thermal stress,thermal deformation and thermo-mechanical coupling stress of the piston under the maximum rate continuous(MRC)operation condition and the overload rate(OR)condition as well as the service life of the piston under creep-fatigue damage were numerically analyzed.The results show that the gap of the piston temperature field and thermal load between simulation and measurement is less than 5%.The creep lifetime of the piston under the MRC is about 46500 h,and the hazard location is located in the high temperature area near the throat of the piston top surface.The fatigue life of the piston under the MRC is about 38400 h,and the hazard area is located at the edge of the contact surface between the piston and the piston rod.However,in the creep-fatigue damage mode,the service life of the piston reduces to 21000 h,54%lower than the pure creep mode and 45%lower than the pure fatigue mode.The hazard area is located in the basin of the combustion chamber on the top of the piston due to high temperature and relatively large thermo-mechanical stress.